1. Field of the Invention
The present invention relates to a system for the deposition of organic films. In particular, the invention relates to a system for the deposition of organic films on substrates by jet printing, where the films may be neat or a mixture of organic materials, such as a host/dopant mixture.
2. Background Information
Thin films of organic materials are used for a variety of organic electronics, such as photovoltaics, organic light emitting devices (OLEDs), and thin film transistors, on research scales and, to a limited extent, on industrial scales. Organic vapor jet printing (OVJP) is a process by which thin organic films may be deposited on a substrate through nozzles. OVJP systems allow localized deposition of organic films on a substrate, typically without the need for masking. It is advantageous to source the OVJP nozzles with a uniform flux (a mixture of organic vapor and a carrier gas) from a source with controllable results.
Organic vapor phase deposition (OVPD) systems, particularly multi-barrel systems, may provide a substantially uniform organic flux with very controllable results. The organic flux of OVPD systems may, e.g., vary by less than 20 mole percent, less than 10 mole percent, or less than 5 mole percent. An example of such a system is found in U.S. Provisional Patent Application Ser. No. 60/965,117, which is expressly incorporated herein in its entirety by reference thereto. Such flux uniformity is desirable in an OVJP system. However, the pressure in OVPD systems may be too low for sourcing OVJP nozzle systems. Contributing to this problem are pressure drops through long run lines between the source (OVPD system) and the nozzles. These pressure drops cause a reduced pressure at the OVJP nozzles, thereby reducing, or potentially preventing, nozzle flow. The pressure drops also cause cold spots in the flux, which may cause premature condensation of the organic flux prior to dispensing from the nozzle. When a relatively low-pressure source, such as an OVPD system, is used, the pressure drops may render the OVJP system inefficient or ineffective.
Another potential problem related to OVJP systems is that the organic material deposited on the substrate may have a profile that resembles a Gaussian curve. In other words, the organic material may significantly taper as the thickness of the film increases, potentially creating a peak of material. It may be advantageous to have a deposition with steeper side walls, i.e., a more “squared” deposition profile in the direction of the nozzle flow. For example, the latter shape may allow a given amount of organic material to be deposited on a smaller area of the substrate, e.g., a silicon wafer. Thus, space on the surface of the substrate may be utilized more efficiently.